Test Handler

ABSTRACT

A test handler is disclosed. The test handler includes first to third transfers for transferring a user tray, and first to third horizontal movement units suitable for respectively moving the first to third transfers in the horizontal direction. The first to third horizontal movement units are independently operated such that each of the first to third transfers can perform independently horizontal movements. Each of the first to third transfers performs based on its previously allocated function, thereby enhancing test process speed for devices.

TECHNICAL FIELD

The present invention relates to a test handler, and more particularlyto a tray transfer apparatus which is capable of transferring a usertray.

BACKGROUND ART

Recently, semiconductor devices (which is hereinafter called a ‘device’)are used in various environments. It is critical for the device to beable to perform even under adverse conditions. Therefore, before sellingthe device on the market, it must undergo tests of how they can performunder adverse conditions. A test handler according to the presentinvention serves to determine whether the states of produced devices aregood or bad under a particular condition, before they are presented tomarket. The procedure referred to above is a method for testing thesedevices.

The technologies related to the test handler are disclosed in: KoreanUtility Model Publication No. 1998-062568 entitled TRAY CATCHER OFHANDLER SYSTEM FOR TESTING SEMICONDUCTOR DEVICE; Korean Utility ModelPublication No. 1998-062567 entitled TRANSFER APPARATUS OF HANDLERSYSTEM; Korean Patent No. 2003-0062702 entitled TRAY TRANSFER APPARATUSOF TEST HANDER FOR SEMICONDUCTOR DEVICE; Korean Patent Publication No.10-2004-0043925 entitled TRAY TRANSFER APPARATUS; Korean Patent No.2002-0031461 entitled TRAY TRANSFER APPARATUS FOR HANDLER; and KoreanPatent No. 2003-0029266 entitled TEST HANDLER. These publicationmaterials disclose structures of test handler in detail.

As disclosed in the publication materials, the test handler includes atray transfer apparatus for transferring a user tray under a transferstandby state to a transfer position as the tray transfer apparatusgrips one of a plurality of user trays loaded in stackers which areinstalled under the loading plates and unloading plates. Then itperforms a movement to transfer the gripped user tray to the loadingplate and unloading plate or the tray transfer apparatus grips a usertray, which is located at the loading plate and unloading plate, toperform a movement to stack the gripped user tray on the stacker. Thepresent invention relates to technical characteristics of the traytransfer apparatus. Here, the word transfer standby state means stateswhere a user tray must be transferred, such as, a state where acorresponding user tray is loaded on the stacker when the user trayincludes a target device to be tested, or a state where a correspondinguser tray is located at the loading or unloading plate immediately afterfinishing a loading or unloading operation. Also, the transfer positionmeans positions to which a user tray under the transfer standby statemust be transferred, such as, a position of a loading plate for a usertray in which a target device to be tested is included, where the usertray is loaded on the stacker, or a position of a unloading plate for anempty user tray which finishes a loading operation in the loading plate.Such concepts will be identically applied to the following description.

FIG. 1 is a block diagram illustrating a tray transfer apparatus 100 ofa conventional test handler. Referring to FIG. 1, the conventional traytransfer apparatus 100 includes a transfer 101 having a pair of grippers11 a and 11 b which selectively grip or un-grip a user tray and a pairof vertical movement units 12 a and 12 b which vertically move the pairof grippers 11 a and 11 b, respectively, a horizontal movement unit 102which horizontally moves the transfer 101, and a controller 103 whichcontrols the pair of vertical movement units 12 a and 12 b and thevertical movement unite 102. The conventional tray transfer apparatus100 was disclosed, in detail, in FIG. 2 and the description relatedthereto in Korean Utility Model Publication No. 1998-062567 (which ishereinafter referred to as cited reference). In the cited reference, thetray transfer apparatus was just expressed as a transfer apparatus and apair of grippers was expressed as a transfer head.

However, since the pair of grippers 11 a and 11 b are independentlymoved in the vertical direction and are always moved together in thehorizontal direction, when events (which means a state where a user trayis in a transfer standby state as the user tray on a loading plate or anunloading plate completely performs a loading or unloading, whosemeaning will be identically applied to the following descriptions)simultaneously occur on the loading plate and the unloading plate, auser tray under a transfer standby state on one of them must keep itsstate. Therefore, the conventional tray transfer apparatus 100 isdisadvantageous in that its process speed decreases.

Also, since the conventional tray transfer apparatus 100 is implementedin a single transfer 101 together with other elements, a pair ofgrippers 11 a and 11 b perform all of transferring operations whilemoving together in the horizontal direction. In addition, because it isdifficult to know that an event occurs at which one of a loading plateor an unloading plate, the conventional tray transfer apparatus cannotperform gripping, moving and waiting operations without precedingprocedures. Namely, the apparatus cannot perform moving and waitingoperations without preceding procedures while it grips a user tray undera transfer standby state. Therefore, the conventional tray transferapparatus is disadvantageous in that the process speed decreases.

In addition, since all of the pairs of grippers 11 a and 11 b must bemoved horizontally from the loading plate section to the unloading platesection, the horizontal movement distance is relatively elongated.Therefore, the conventional tray transfer apparatus is disadvantageousin that the process speed decreases.

The above-mentioned problems are more seriously shown in this fieldbecause technologies for test handlers will be developed such that thetest handlers can process devices with large capacity.

DISCLOSURE OF INVENTION Technical Problem

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide a testhandler including three transfers each of which has a gripper and avertical movement unit suitable for moving the gripper in the verticaldirection, where the three transfers can move independently in thehorizontal direction.

It is another object of the present invention to provide a test handlerincluding three transfers which can independently move in the horizontaldirection. The respective three transfers are assigned by respectivefunctions, such that previously-allocated procedures can be performed bythem respectively before generation of an event, thereby reducing themovement distances of the respective transfers.

Technical Solution

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of a test handlertest handler including first to third transfers and first to thirdhorizontal movement devices. Each transfer includes a gripper suitablefor selectively gripping and un-gripping a user tray; and a verticalmovement unit suitable for moving the gripper in the vertical direction,wherein the first to third transfers are aligned in the horizontaldirection in that order. The first to third horizontal movement unitsare suitable for respectively moving the first to third transfers in thehorizontal direction, wherein the first to third horizontal movementunits can be independently operated.

Preferably, the first transfer performs a horizontal movement within afirst section, and the third transfer performs a horizontal movementwithin a third section, which is separated from the first section.Therefore, the horizontal movement distance of each transfer can bereduced, and thus the transfer speed of the user tray is rapid.

In accordance with another aspect of the present invention, there isprovided to a test handler including first to third transfers. Here, thefirst transfer is suitable for gripping a first subject user tray thathas therein a plurality of target devices to be tested, and then puttingthe first subject user tray onto one of loading plates. The secondtransfer is suitable for gripping a second subject tray from one of theloading plates after the second subject user tray is made empty bytransferring a plurality of target devices therein to a test tray, andthen putting the second subject user tray onto one of unloading plates.The third transfer is suitable for gripping a third subject user trayfrom one of the unloading plates after a plurality of tested devices areloaded therein, and then stacking the third subject user tray in one ofstackers, wherein the first to third transfers can be independentlymoved in the horizontal direction.

Preferably, the first transfer waits near the loading plates aftergripping the first subject user tray having therein a plurality oftarget devices to be tested, while the second transfer is gripping thesecond subject user tray, having been made empty, from one of theloading plates; and then the first transfer puts the first subject usertray onto the one of the loading plates after second transfer finishesgripping the second subject user tray.

Preferably, the second transfer waits near the unloading plate aftergripping the second subject user tray having been made empty, while thethird transfer is gripping the third subject user tray, having aplurality of tested devices loaded therein, from one of the unloadingplates; and then the second transfer puts the second subject user trayonto the one of the unloading plates after the third transfer finishedgripping the third subject user tray.

In accordance with further aspect of the present invention, there isprovided to a test handler including first to third transfers. Here, thefirst transfer is suitable for: gripping a first user tray from astacker, the first user tray having therein a plurality of targetdevices to be tested; waiting near loading plates while still grippingthe first user tray; putting the first user tray onto one of the loadingplates after an empty user tray is removed from the one of loadingplates; moving towards the stacker again to grip another first user trayhaving therein a plurality of target devices to be tested; waiting nearthe loading plates while still gripping the another first user tray. Thesecond transfer is suitable for: waiting near unloading plates whilegripping a second user tray from one of the loading plates, the seconduser tray having been made empty by transferring a plurality of targetdevices therein to a test tray; putting the second user tray onto one ofthe unloading plates after a loaded user tray having a plurality oftested devices loaded therein is removed from one of the unloadingplate; waiting again near the loading plates to grip another second usertray from one of the loading plates The third transfer is suitable for:waiting near the unloading plates; gripping a third user tray from oneof the unloading plates, the third user tray having a plurality oftested devices loaded thereto; waiting again near the unloading platesto grip another third user tray from one of the unloading plates, Here,the first to third transfers can be independently moved in thehorizontal direction.

In accordance with still further aspect of the present invention, thereis provided to a test handler including at least two transfers forrespectively transferring a user tray under a transfer standby state toa target position, at least two horizontal movement units, and acontroller. Here, each transfer includes: a gripper suitable forselectively gripping and un-gripping a user tray; and a verticalmovement unit suitable for moving the gripper in a vertical direction.At least two horizontal movement units is prepared corresponding to theat least two transfers for horizontally moving the at least twotransfers, respectively. The controller independently controlsoperations of at the least two vertical movement units respectivelyprovided for the at least two transfers and makes the at least twohorizontal movement units can be independently operated from each other,thereby enabling the at least two transfers to independently performhorizontal movements.

Preferably, the at least two transfers include a first transfer suitablefor transferring a first user tray from a stacker to one of the loadingplates; a second transfer suitable for transferring a second user trayfrom one of the loading plates to one of unloading plates after thesecond user tray on the one of the loading plates has been made empty bytransferring a plurality of target devices therein to a test tray; and athird transfer suitable for transferring a third user tray from one ofthe unloading plates to one of stackers after a plurality of testeddevices has been loaded into the third user tray on the unloading plate.

In accordance with yet another aspect of the present invention, there isprovided to a test handler including at least two transfers, at least ntwo horizontal movement units, and a controller. Here, the at least twotransfers are configured such that they can be moved within differenthorizontal movement sections, respectively, to transfer a user trayunder a transfer standby state to a transfer position. The at least twohorizontal movement units are installed corresponding to the at leasttwo transfers, such that they can horizontally move the at least twotransfers within horizontal movement sections in which the transfers arelocated, respectively.

ADVANTAGEOUS EFFECTS

As apparent from the above description, the present invention provides atest handler including three transfers each of which has a gripper and avertical movement unit which moves the gripper in the verticaldirection, where the three transfers independently move in thehorizontal direction, each transfer has a function such that a previousprocedure can be performed before an event occurs, and horizontalmovement distance is divided on the basis of functions of the respectivetransfers such that the respective transfers can move quickly, therebyenhancing process speed thereof due to movement of user trays.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a block diagram illustrating a tray transfer apparatus of aconventional test handler;

FIG. 2 is a perspective view illustrating primary parts of a testhandler according to the present invention;

FIG. 3 is a block diagram illustrating primary parts of the test handleraccording to the present invention; and

FIG. 4 to FIG. 6 are views illustrating operation states of the testhandler according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be now described in detail with reference tothe accompanying drawings, in which preferred embodiments of the presentinvention are shown.

FIG. 2 is a perspective view illustrating primary parts of a testhandler according to the present invention, and FIG. 3 is a blockdiagram illustrating primary parts of the test handler according to thepresent invention.

Referring to FIG. 2 and FIG. 3, the test handler according to thepresent invention includes three transfers 200′, 200″, and 200′″, threehorizontal movement units 300′, 300′″, and 300′″, and a controller. Thethree transfers 200′, 200″, and 200′″ transfer user trays under atransfer standby state to a transfer position, and the three horizontalmovement units 300′, 300″, 300′″ independently move the three transfers200′, 200″ and 200′″ in the horizontal direction. On the other hand,symbol ‘T,’ which is not described in detail, indicates an installationplate on which all of the elements are installed.

The following will describe the configuration of the test handler indetail.

The three transfers 200′, 200″, and 200′″ will be renamed as follows:reference numeral 200′ is referred to as a first transfer suitable forperforming a movement operation within a first section A; referencenumeral 200″ is referred to as a second transfer suitable for performinga movement operation within a second section B; and 200″ is referred toas a third transfer suitable for performing a movement operation withina third section C. Each of the first to third transfers 200′, 200″ and200′″includes a gripper 21 suitable for selectively gripping andun-gripping a user tray, and a vertical movement unit 22 suitable formoving the gripper 21 in the vertical direction.

The gripper 21 will not be fully described in this application becausethe configuration thereof was described in the cited reference indetail.

The vertical movement unit 22 includes a vertical guide rail 22 aenabling the gripper 21 to move up and down in the vertical directiontherealong, a motor 22 b supplying mechanical power thereto such thatthe gripper 21 can perform a vertical direction movement. Also, in orderto transfer the mechanical power of the motor 22 b to the gripper 21,the vertical movement unit 22 includes a transfer shaft 22 c, a pulley22 d installed at one end of the transfer shaft 22 c, a motor pulley 22e installed at the rotation shaft of the motor 22 b, and a belt 22 fconnecting the pulley 22 d to the motor pulley 22 e. In addition, thevertical movement unit 22 further includes a holding plate 22 g holdingthe vertical guide rail 22 a. Therefore, the vertical movement unit 22enables the gripper 21 to move up and down as the mechanical power ofthe motor 22 b is transferred to the gripper 21 through the motor pulley22 e, pulley 22 d and transfer shaft 22 c, according to forward andbackward rotations of the motor 22 b.

Although the gripper 21 and the vertical movement unit 22 are installedat each of the first to third transfers 200′, 200″ and 200′″, the othergrippers and vertical movement units of the first to third transfers200′, 200″ and 200′″ are numbered by the same figures as 21 and 22 inFIG. 2, for brief description.

On the other hand, the three horizontal movement units 300′, 300″, and300′″ will be renamed as follows: reference numeral 300′ is referred toas a first horizontal movement unit which can move the first transfer200′ in the horizontal direction within the first section A; referencenumber 300″ is referred to as a second horizontal movement unit whichcan move the second transfer 200″ in the horizontal direction within thesecond section B, and reference numeral 300′″ is referred to as a thirdhorizontal movement unit which can move the third transfer 200′″ in thehorizontal direction within the third section C.

More specifically, the first horizontal movement unit 300′ horizontallymoves the first transfer 200′ within the first section A such that thefirst transfer 200′ can transfer a user tray (not shown) under atransfer standby state onto the loading plate. The user tray includesone of a plurality of target devices to be tested (not shown), which arestacked on a stacker (not shown). The stacker is located under theloading plate. To this end, the first horizontal movement unit 300′includes: horizontal guide rails 31 a and 31 b which guide a holdingplate 22 g of the first transfer 200′ such that the holding plate 22 gcan perform a horizontal movement; a first motor 32′ supplyingmechanical power for the horizontal movement of the first transfer 200′thereto; a first a pulley 33′a installed to the rotation shaft of thefirst motor 32′; a first b pulley 33′b installed to a correspondingplace which is apart from the first a pulley 33′a in the horizontaldirection; and a first belt 34′ connecting the first a pulley 33′a, thefirst b pulley 33′b and the holding plate 22 g of the first transfer200′ to each other. Here, as shown in FIG. 2, the first a pulley 33′a islocated at one end of the first section A and the first b pulley 33′b islocated at the other end.

The second horizontal movement unit 300″ horizontally moves the secondtransfer 200″ within the second section B in the horizontal direction,such that the second transfer 200″ can transfer an empty user tray undera transfer standby state on the loading plate from a gripping positionto a transfer position where the empty user tray on an unloading plateis located. Here, the second section B is from the gripping position tothe transfer position. To this end, the second horizontal movement unit300″ includes: horizontal guide rails 31 a and 31 b which guide aholding plate 22 g of the second transfer 200″ such that the holdingplate 22 g can perform a horizontal movement; a second motor 32″supplying mechanical power for the horizontal movement of the secondtransfer 200″ thereto; a second a pulley 33″a installed to the rotationshaft of the second motor 32″; a second b pulley 33″b installed to acorresponding place which is apart from the second a pulley 33″a in thehorizontal direction; and a second belt 34″ connecting the second apulley 33″a, the second b pulley 33″b and the holding plate 22 g of thesecond transfer 200″ to each other. Here, as shown in FIG. 2, the seconda pulley 33″a is located at one end of the second section B and thesecond b pulley 33″b is located at the other end. Although the presentembodiment is implemented such that first to third horizontal movementunits can share the horizontal guide rails 31 a and 31 b, person skilledin the art will easily appreciate that the embodiment can be modifiedsuch that each of the horizontal movement units can employ therespective horizontal guide rails.

The third horizontal movement unit 300′″ horizontally moves the thirdtransfer 200′″within the third section C, such that the third transfer200′″ can transfer a user tray (on which test-finished devices areincluded) from a position on an unloading plate to a transfer position,while the tray is under a transfer standby state, such that thetest-finished devices can be loaded to a stacker installed under theunloading plate. To this end, the third horizontal movement unit 300′″includes: horizontal guide rails 31 a and 31 b which guide a holdingplate 22 g of the third transfer 200′″ such that the holding plate 22 gcan perform a horizontal movement; a third motor 32′″ supplyingmechanical power for the horizontal movement of the third transfer 200′″thereto; a third a pulley 33′″a installed to the rotation shaft of thethird motor 32′″; a third b pulley 33′″b installed to a correspondingplace which is apart from the third a pulley 33′″a in the horizontaldirection; and a third belt 34′″ connecting the third a pulley 33′″a,the third b pulley 33′″b and the holding plate 22 g of the thirdtransfer 200′″ to each other. Here, as shown in FIG. 2, the third apulley 33′″a is located at one end of the third section C and the thirdb pulley 33′″b is located at the other end.

The first to third horizontal movement units 300′, 300″ and 300′″ areoperated such that: when the respective first to third motors 32′, 32″and 32′″ are operated according to control of the controller 400,corresponding pulleys (33′a, 33′b; 33″a, 33″b; 33′″a, 33′″b) and belts(34′; 34″; 34′″) are also operated together, and accordingly the holdingplate 22 g of each of the first to third transfers 200′, 200″ and 200′″is guided by the horizontal guide rails 31 a and 31 b, thereby smoothlymoving the first to third transfers 200′, 200″ and 200′″ in thehorizontal direction.

On the other hand, the controller 400 controls operations of the motor22 b of the vertical movement unit 22 and the first to third motors 32′,32″ and 32′″ of the first to third horizontal movement units 300′, 300″and 300′″ to control operations of the first to third transfers 200′,200″ and 200′″.

The following is a description for operations of the first to the firsttransfers 200′, 200″ and 200′″ which are controlled by the controller400 as the test handler starts. For convenient description, each of thefirst to the first transfers 200′, 200″ and 200′″ will be described,referring to FIG. 4 to FIG. 6 in which only a horizontal movementdistance is illustrated.

Operation of First Transfer—FIG. 4

The first transfer 200′ grips a user tray 81 that has therein aplurality of target devices to be tested, which is under a transferstandby state, from a stacker 71 located under a loading plate 61, andthen waits near the loading plates 61, in step S41 (a gripper 21 isillustrated as it is located beside the left of the loading plate 61 asshown in FIG. 4) while the second transfer 200″, whose description willbe described in detail later, is gripping an empty user tray from one ofthe loading plates 61. Afterward, the first transfer 200′ puts thegripped user tray 81 onto the one of the loading plates 61, in step S42,after the second transfer 200″ finishes gripping the empty user tray.After that, the first transfer 200′ repeats its operation within thefirst section.

Operation of Second Transfer—FIG. 5

The second transfer 200″ grips an empty user tray under a transferstandby state from one of the loading plates 61, where the empty usertray is prepared as the plurality of the target devices to the test trayare transferred to the test tray, and then waits near the unloadingplates 62, in step S51 (a gripper 21 is illustrated as it is locatedbeside the left of one of the unloading plates 62 as shown in FIG. 5),while the third transfer 200′″ (described in detail later) is gripping auser tray, having a plurality of tested devices loaded therein, from oneof the unloading plates 62. Afterwards, the second transfer 200″ putsthe gripped empty user tray onto the one of the unloading plates 62, instep S52, after the third transfer 20′″ finishes gripping the user tray.After that, the second transfer 200″ moves near one of the loadingplates 61, again, and waits for the next operation, in step S53 (thegripper 21 is illustrated, in FIG. 5, as it is located beside the rightof one of the loading plates). Then, the second transfer 200″ repeatsits operations within the second section.

On the other hand, when an event occurs in a state where all of thedevices, which are included in the user tray on the loading plate 61,are not loaded onto the test tray, the second transfer 200″ loads acorresponding user tray onto a stacker numbered by 74. Namely, such anoperation is performed to prevent that the corresponding user tray moveson the unloading plate while a device remains on the corresponding usertray on the loading plate 61. Here, the embodiment may be modified suchthat an additional space can receive the corresponding user tray.

Also, when an event occurs on one of the unloading plates 62 while anyevent does not occur on one of the loading plates 61, the secondtransfer 200′ grips an empty user tray from a stacker numbered by 73, inwhich empty user trays are stacked, and then transfers the empty usertray onto one of the unloading plates 62 in which the event occurred.Therefore, the unloading operation is smoothly performed without delay.

Operation of Third Transfer—FIG. 6

While the third transfer 200′″ waits near one of the unloading plates 62(the gripper 21 waits beside the right of one of the unloading plates 62in FIG. 6), when a user tray is shown, where the user tray is under atransfer standby state as the target devices are unloaded to the testtray, the unloaded user tray is gripped, in step S62, and then loaded ona stacker 72 located under one of the unloading plates 62, in step S62.After that, the third transfer 200′″ repeats its operation within thethird section.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, the test handlerenhances process speed of user trays based on improvement of movement ofthe user trays, the present invention can be properly applied to thefield of testing semiconductor devices.

1-8. (canceled)
 9. A test handler comprising: a plurality of transferseach including a gripper for selectively gripping and un-gripping a usertray and a vertical movement unit for moving the gripper in the verticaldirection, wherein the plurality of transfers are aligned in ahorizontal direction in that order; and a plurality of horizontalmovement units for respectively moving the plurality of transfers in ahorizontal direction, wherein the plurality of horizontal movement unitscan be independently operated.
 10. The test handler according to claim9, wherein a first transfer of the plurality of transfers performs ahorizontal movement within a first section, and a third transfer of theplurality of transfers performs a horizontal movement within a thirdsection, which is separated from the first section.
 11. A test handlercomprising: a first transfer for gripping a first user tray that hastherein a plurality of target devices to be tested, and then putting thefirst user tray onto one of loading plates; a second transfer forgripping a second user tray from one of the loading plates after thesecond user tray is made empty by transferring a plurality of targetdevices therein to a test tray, and then putting the second user trayonto one of unloading plates; and a third transfer for gripping a thirduser tray from one of the unloading plates after a plurality of testeddevices are loaded therein, and then stacking the third user tray in oneof stackers.
 12. The test handler according to claim 11, wherein thefirst transfer, the second transfer and the third transfer can beindependently moved in the horizontal direction.
 13. The test handleraccording to claim 12, wherein the first transfer waits near the loadingplates after gripping the first user tray having therein a plurality oftarget devices to be tested, while the second transfer grips the seconduser tray, having been made empty, from one of the loading plates, andthen the first transfer puts the first user tray onto the one of theloading plates after second transfer finishes gripping the second usertray.
 14. The test handler according to claim 12, wherein the secondtransfer waits near the unloading plate after gripping the second usertray having been made empty, while the third transfer grips the thirduser tray, having a plurality of tested devices loaded therein, from oneof the unloading plates, and then the second transfer puts the seconduser tray onto the one of the unloading plates after the third transferfinishes gripping the third user tray.
 15. The test handler according toclaim 13, wherein the second transfer waits near the unloading plateafter gripping the second user tray having been made empty, while thethird transfer grips the third user tray, having a plurality of testeddevices loaded therein, from one of the unloading plates, and then thesecond transfer puts the second user tray onto the one of the unloadingplates after the third transfer finishes gripping the third user tray.16. A test handler comprising: a first transfer for gripping a firstuser tray from a stacker, the first user tray having therein a pluralityof target devices to be tested, for waiting near loading plates whilestill gripping the first user tray, for putting the first user tray ontoone of the loading plates after an empty user tray is removed from theone of loading plates, for moving towards the stacker again to gripanother first user tray having therein a plurality of target devices tobe tested, and for waiting near the loading plates while still grippinganother first user tray; a second transfer for waiting near unloadingplates while gripping a second user tray from one of the loading plates,the second user tray having been made empty by transferring a pluralityof target devices therein to a test tray, for putting the second usertray onto one of the unloading plates after a loaded user tray having aplurality of tested devices loaded therein is removed from one of theunloading plate, and for waiting again near the loading plates to gripanother second user tray from one of the loading plates; and a thirdtransfer for waiting near the unloading plates, for gripping a thirduser tray from one of the unloading plates, the third user tray having aplurality of tested devices loaded thereto, and for waiting again nearthe unloading plates to grip another third user tray from one of theunloading plates, wherein the first to third transfers can beindependently moved in a horizontal direction.
 17. A test handlercomprising: at least two transfers for respectively transferring a usertray under a transfer standby state to a target position, each transferincluding a gripper for selectively gripping and un-gripping a user trayand a vertical movement unit for moving the gripper in a verticaldirection; at least two horizontal movement units prepared to correspondto the at least two transfers for horizontally moving the at least twotransfers, respectively; and a controller for independently controllingoperations of at least two vertical movement units respectively providedfor the at least two transfers and making the at least two horizontalmovement units operate independently from each other, thereby enablingthe at least two transfers to independently perform horizontalmovements.
 18. The test handler according to claim 17, wherein the atleast two transfers comprise: a first transfer for transferring a firstuser tray from a stacker to one of the loading plates; a second transferfor transferring a second user tray from one of the loading plates toone of unloading plates after the second user tray on the one of theloading plates has been made empty by transferring a plurality of targetdevices therein to a test tray; and a third transfer for transferring athird user tray from one of the unloading plates to one of stackersafter a plurality of tested devices has been loaded into the third usertray on the unloading plate.
 19. A test handler comprising: a firsttransfer for gripping a user tray from a stacker, the user tray havingtherein a plurality of devices to be tested, for waiting near loadingplates while still gripping the user tray, for putting the user trayonto one of the loading plates from which an empty user tray is removed,for moving towards the stacker again to grip another user tray havingtherein a plurality of devices to be tested, and waiting near theloading plates while still gripping another user tray.